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THEME PARKS IN SO CAL
These are the big three theme parks in So Cal; I did not put Universal Studios or Disneyland in here as they really do not qualify to me as "coaster" parks. I will have a separate section for other theme parks in So Cal in the future.

Knott's Berry Farm-although this website wins my award for "least frequently updated website of the year", it is your official source of information for the park. I admit, Knott's is one of my favorites as they have three out of my top five coasters, the atmosphere is great, and they beat Magic Mountain for food hands down. They are also close enough that I can go there more often and have the best Halloween event of any of the theme parks.
Six Flags Magic Mountain-if you want to bypass the infectiously catchy theme song by the Vengaboys and the animation of the dancing Mr. Six, just click "Park Info". As far as coasters go, this place has the biggest selection and the most. As far as atmosphere, although the landscaping and location are nice, a lot of things need work, and I'm sorry, but the food service is atrocious; I have yet to have a positive culinary experience at this park. However, they have the other two coasters in my top 5, X and Scream.
Disney's California Adventure-Disneyland is not to me a "coaster" park (although they have some fun coaster type rides), and this is intended to be a mostly roller coaster website. California Adventure is not really a coaster or thrill park either, but they do have two decent coaster rides that are worth a spin, even if the "thrills" are a little watered down. Disney and California Adventure are great parks, just not enough extreme thrill rides for my personal taste. Still can be a lot of fun though.
OTHER GREAT THEME PARKS OUTSIDE CALIFORNIA
These are a few theme parks outside of California I have visited; these are not all of them, but these are the ones that really stood out as having a great collection of rides and that offered an overall good experience.

Silver Dollar City-this is not the biggest theme park, nor do they have the biggest selection of rides, but as far as atmosphere, food, attention to detail and offering a "family" park experience that offers something for the thrillseekers in the family as well as the younger ones, these guys have it down. Not a lot of coasters, but some great ones (Wildfire, Thunderation and the newest one, Powder Keg) and the setting is about as beautiful as you will get for a theme park. As far as parks deisgned with the whole family in mind go, I think this park does it better than the Disney Parks do.
Six Flags Great America-haven't been there in a very long time, but in that time the park has only gotten better. This park serves the Windy City as well as Milwaukee, and offers a fantastic selection of coasters as well as decent theming and a free waterpark, if you're into that sort of thing. Even though it is over 20 years old, The Demon is still a great steel coaster and this park was also where the famous "Batman" coaster had its first installation. I really want to get back here and get a ride in on the Raging Bull, as it looks to be great.
Worlds Of Fun-owned by the people who own Knott's, Cedar Point and Dorney Park, this is a park I remember fondly from my high school days. Unfortunately, two awesome coasters have been taken out of the park in recent years (and since I have been there)-the Zambezi Zinger and the Orient Express. That being said, they still have some great rides and are said to be adding a huge new coaster in the coming two years. In the days when I did water parks, I used to spend many hours at the adjacent Oceans of Fun park as well.
 
 
OTHER COASTER SITES
These are websites for those into coasters and theme parks; some are diehard enthusiasts, some are rumor mills for new rides, and some are just groups of people who are not hardcore enthusiasts but just love the rides, and some are all of the above.

Westcoaster -my favorite of all the coaster and amusement park themed sites I frequent. Not only that, a very cool bunch of people. I post on the boards as Jhcbiinoc, and have been to a few of their meets and events. Real people with a sense of humor.
RideWorld-I just joined recently, and am glad I did. In addition to a very reasonable annual membership, there is a lot to see here and have met Chris, who runs the site, really nice guy. RideWorld put together the excellent West Coast Bash in March at SFMM.
Coaster Realm Network-Good site, and several of the people who run and work on it were cool enough to let me hang out with them at the most recent Coaster Solace. Cool photo updates with a definite sense of humor.